1. Field of the Invention
This invention relates broadly to devices used in ophthalmology and optometry. More particularly, this invention relates to devices for the administration of topical medicines to the ocular surface.
2. State of the Art
During the preparation of a patient for ocular surgery, e.g. cataract surgery, the eye is usually treated with medication to anaesthetize the eye. Typically, anaesthesia is injected behind the eye with a needle. However, inserting a needle behind the eye requires a skilled surgeon or anesthesiologist and has inherent dangers. For example, the globe or nerve of the eye may be perforated by the needle resulting in catastrophic vision loss. In addition, because the eye is numb and blinded for several hours, the eye has to be patched postoperatively.
One potential alternative without the dangers of needle administration, and which does not require post-operative patching, is simply to provide topical medicines to the tear film of the eye and have the medication be absorbed into the eye through the tear film. Recently, so called "topical anaesthesia" has become increasingly popular.
However, conventional topical administration of medicines has several drawbacks. First, only a relatively small volume of the total volume of a drop is provided to the tear film. The majority of the drop, as soon as it is applied, either runs down the cheek, or drains and is actively pumped through the naso-lacrimal duct system. Because the drops run or drain away from the eye, multiple applications of drops are required, e.g., every five minutes during the thirty minutes prior to examination or surgery. In addition, multiple drops are required because the tear film is continually replaced with fresh tears from the lacrimal gland and other accessory tear glands. Second, drops intended for the tear film and ocular surface, but which enter the naso-lacrimal duct system can have serious systemic side effects when absorbed through the lacrimal sac and nasopharynx. The multiple application of drops increases undesirable system absorption. Third, the multiple application of drops is an inefficient use of staff labor and causes discomfort to the patient prior to surgery. Fourth, there are economic disadvantages inherent in the inefficient administration of drops; i.e., a substantial volume of each drop running down the patient's cheek, given the high cost of these medicines.
As a result, there has been activity in the field of ocular medicinal and anaesthetic administration to better provide topical medicines to the eye and to provide for their sustained release. For example, and as shown in prior art FIG. 1, which is representative of U.S. Pat. No. 3,618,604 to Ness, an ocular insert 10 is positioned in the fornix 12 of the eye between the sclera 16 and the lower lid 18. The insert 10 has imperforate walls 20 which hold a drug. When the insert is placed into the eye, the drug diffuses through the walls and into the eye. However, the insert is difficult to manufacture, can rupture or leak, and would need to be pre-manufactured with the drug inside the walls (and is therefore not adaptable to releasing a particular dose of medicine, as prescribed by a physician, if the insert is not manufactured with such dosage). In addition, it is difficult to control and obtain desired release rates. Moreover, the amount of medicine that can be held by the insert is limited to the size of an insert which can be held in the fornix of the eye of a patient. Similar devices are disclosed in U.S. Pat. No. 3,916,899 to Theeuwes et al., U.S. Pat. No. 4,014,335 to Arnold, and U.S. Pat. No. 5,378,475 to Smith et al., each suffering from all or several of the drawbacks described above.
Another device for the administration of medicine is the Bloomberg Ophthalmic Ring.TM. sold by Oasis Medical and Ultracell Medical Technologies, and represented in prior art FIG. 2. The Bloomberg Ophthalmic Ring.TM. is a ring 30 of absorbent material which can be soaked in a medicine, e.g., an anaesthetic. With respect to anaesthesia, the ring-shaped design concentrates the anaesthesia in the desired locations; i.e., at the deep ciliary nerves and conjunctiva nerves, providing a profound anaesthetic effect. However, the ring does not hold much anaesthetic (or other medicine) and more anaesthetic may be required during surgery. Once the eye has absorbed the medicine from the ring, the ring can be resaturated using a syringe. Therefore, while the Bloomberg Ophthalmic Ring.TM. does not require replacement after the medicine has diffused out of the ring, as the ring can be resaturated, the ring nevertheless suffers from having a limited initial capacity. In addition, extreme care must be taken while injecting additional anaesthetic into the ring. Moreover, the rate at which medicine diffuses out of the ring is also difficult to control. Further, the ring must be in contact with the eye during ocular surgery, and thus often creates a physical obstacle to the surgeon at the time of surgery.